Study On The Degradation Of Mixed Dyes By Green Synthesis Of Nano Zero-valent Iron And Expanded Perlite Loaded Nano Zero-valent Iron

The industry of printing and dyeing have developed rapidly in China,meanwhile dye wastewater discharged also increases.However,such wastewater has intense color,high toxicity,high concentrated substrate,and their intermediate metabolites are characterized by poor biodegradation,mutagenicity,and carcinogenicity.Dye wastewater has great harm to human health,aquatic life and natural water environment.Therefore,at present,it is a hot research topic in the restoration of water.As efficient environmental remediation material,nanometer zero-valent iron?nZVI?widely used in remediation of water and soil pollution.In research,two kinds of nZVI were prepared:green synthesis of nanometer zero-valent iron?GS-nZVI?were prepared from grape seed extract and supported nano-zero-valent iron supported by expanded perlite as carrier?P-nZVI?.The degradation of azo mixed dyes?acid red and methyl orange?was studied by using two kinds of nZVI.?1?GS-nZVI combined with H₂O₂ degrade mixed dyesThe green synthesized nano zero valent iron?GS-nZVI?,prepared by grape seed extract,used as the catalyst of Fenton-like system to degrade mixed dye solution.The characterization of GS-nZVI by scanning electron microscopy?SEM?,X-ray photoelectron spectroscopy?XPS?,X-ray diffraction?XRD?and Fourier Transform Infrared spectrometer?FTIR?.The results showed that the nZVI particles with size between 20-100nm were successfully prepared and he surface of GS-nZVI was coated with polyphenols before and after the reaction,which reduced the aggregation and oxidation of GS-nZVI.The effects of pH vale,reaction temperature,the concentration of Fe²⁺and the amount of H₂O₂ on the degradation of mixed dyes were investigated respectively.The results shown,with the decrease of pH and the increase of temperature,the mixed dyes can be degraded better;in range of the experiment,the degradation efficiency of mixed dyes were the best when the concentration of H₂O₂ was 10 wt.%.The highest degradation rates of acid red and methyl orange dyes in mixed solution were 98.7%and 99.4%.At unadjusted value of pH?pH=6.8?,the degradation rates of acid red and methyl orange in mixed solution were 94.43%and 97.49%respectively by GS-nZVI/H₂O₂ Fenton-like method and 47.80%and the degradation rate of traditional Fenton method were 47.80%and 71.84%respectively.The natural water is usually neutral,therefore,the GS-nZVI/H₂O₂ Fenton-like method can maintain a good degradation effect in natural water,The results of degradation kinetic analysis show,the pseudo first order modeland the pseudo second order model can be used to describe the degradation behavior of mixed dye by the Fenton-like method.The simulation results of pseudo first order kinetic model are better.It indicating that the process includes chemical oxidation degradation and adsorption,and the chemical degradation is the main factor.The study of adsorption kinetics shows,the adsorption process is more related to the pseudo second order adsorption modeland the internal diffusion model was used to analyze the adsorption process.This indicates that adsorption is mainly chemisorption and consists of liquid diffusion and intra-particle diffusion.The results of thermodynamic analysis indicate that?G⁰<0,?H⁰>0,?S⁰>0,and the degradation of mixed dye is a spontaneous and endothermic process,and the whole system is increasing entropy.The change of UV–Vis absorption spectrum shows that the degradation of mixed dye is very effective by the GS-nZVI/H₂O₂ Fenton-like method.?2?Study on expanded perlite support nano zero valent iron degrade mixed dyes.Supported nano zero valent iron was prepared by using expanded perlite,and the degradation of mixed dyes?acid red and methyl orange dyes?was studied.The characterization of P-nZVI by scanning electron microscopy?SEM?and X-ray diffraction?XRD?.The results showed that the nZVI particles have spherical structure and the particle size is between 5-70nm,and the nZVI particles are well-proportioned attached to the surface of expanded perlite.The effects of the dosage of P-nZVI,pH vale,reaction temperature,and the initial concentration of mixed solution on the degradation of mixed dyes were investigated respectively.The result shows,the optimum loading ratio of nanometer zero-valent iron and expanded perlite is 1:2;the efficiency of degradation improved with the decrease of pH,the raise of temperature and the reduction of initial concentration.When the concentration of acid red and methyl orange in mixed dye solution is 100mg/L,the pH is not adjusted?pH=6.8?,the reaction temperature is 303.15K and the dosage of P-nZVI was2g/L,the degradation rates of acid red and methyl orange dyes were 99.01%and 98.78%respectively.The results of kinetic analysis shows,the reduction degradation behavior of mixed dye by P-nZVI accord with the pseudo first order kinetic model and pseudo second order kinetic model at the same time.It shows that the degradation process is coexisting with reduction degradation and adsorption.The apparent activation energies of acid red and methyl orange are 36.91kJ·mol^-1and 73.78 kJ·mol^-1 respectively,and it shows that the degradation process is mainly a surface-controlled reaction.The study of adsorption kinetics shows,the adsorption process is more related to the pseudo second order adsorption model.It indicates that the reduction degradation reaction and chemisorption reaction coexist in the degradation process.The results of thermodynamic analysis indicate that?G⁰<0,?H⁰>0,?S⁰>0,and the degradation of mixed dye is a spontaneous and endothermic process,and the whole system is increasing entropy.The change of UV–Vis absorption spectrum shows that P-nZVI can effectively decolorize the mixed dyes.The discussion on degradation mechanism:In summary,GS-nZVI combined with H₂O₂ oxidation to degrade mixed dyes,and P-nZVI direct reduction degradation of mixed dyes.Two methods of degradation mechanism are different,but they can achieve very well degradation effect.